Document falsification and product counterfeiting are significant problems that have been addressed in a variety of ways. One of the more successful approaches has been the use of latent or hidden images applied to or printed on objects to be protected. These images are generally not viewable without the assistance of specialized devices that render them visible.
One approach to the formation of a latent image is to optically encode the image so that, when printed, the image can be viewed only through the use of a corresponding decoding device. Such images may be used on virtually any form of printed document including legal documents, identification cards and papers, labels, currency, stamps, etc. They may also be applied to goods or packaging for goods subject to counterfeiting.
Objects to which an encoded image is applied may be authenticated by decoding the encoded image and comparing the decoded image to an expected authentication image. The authentication image may include information specific to the object being authenticated or information relating to a group of similar objects (e.g., products produced by a particular manufacturer or facility). Production and application of encoded images may be controlled so that they cannot easily be duplicated. Further, the encoded image may be configured so that tampering with the information on the document or label is readily apparent.
Authentication of documents and other objects “in the field” has typically required the use of hardware decoders such as lenticular or micro-array lenses that optically decode the encoded images. These lenses must have optical characteristics that correspond to the parameters used to encode and apply the authentication image and must be properly oriented in order for the user to decode and view the image.
Because they can only be used for encoded images with corresponding characteristics, hardware decoders are relatively inflexible tools. There are also circumstances where the use of an optical decoder to decode encoded images is impractical or undesirable. For example, authentication using an optical decoder requires immediate on-site comparison of the decoded image to the authentication image. This requires that the on-site inspector of the object being authenticated must be able to recognize differences between the decoded image and the expected authentication image. This is impractical in instances where there are many possible variations in the expected authentication image. It also may be undesirable for the on-site inspector to have access to information that may be embedded in the decoded image. Finally, real-time viewing using a typical hardware decoder does not produce a hard copy image that can be retained for future use. Any later investigation must rely on the viewer for evidence of the initial object inspection.